Radiation induces osteogenesis in human aortic valve interstitial cells

Targeted Radiation Exposure Induces Accelerated Aortic Valve Remodeling in ApoE-/- Mice

Thoracic radiation therapy may result in accelerated atherosclerosis and in late aortic valve stenosis (AS). In this study, we assessed the feasibility of inducing radiation-induced AS using a targeted aortic valve irradiation (10 or 20 Grays) in two groups of C57Bl6/J (WT) and ApoE-/- mice compared to a control (no irradiation). Peak aortic jet velocity was evaluated by echocardiography to characterize AS. T2*-weighted magnetic resonance imaging after injection of MPIO-αVCAM-1 was used to examine aortic inflammation resulting from irradiation. A T2* signal void on valve leaflets and aortic sinus was considered positive. Valve remodeling and mineralization were assessed using von Kossa staining. Finally, the impact of radiation on cell viability and cycle from aortic human valvular interstitial cells (hVICs) was also assessed. The targeted aortic valve irradiation in ApoE-/- mice resulted in an AS characterized by an increase in peak aortic jet velocity associated with valve leaflet and aortic sinus remodeling, including mineralization process, at the 3-month follow-up. There was a linear correlation between histological findings and peak aortic jet velocity (r = 0.57, p < 0.01). In addition, irradiation was associated with aortic root inflammation, evidenced by molecular MR imaging (p < 0.01). No significant effect of radiation exposure was detected on WT animals. Radiation exposure did not affect hVICs viability and cell cycle. We conclude that targeted radiation exposure of the aortic valve in mice results in ApoE-/-, but not in WT, mice in an aortic valve remodeling mimicking the human lesions. This preclinical model could be a useful tool for future assessment of therapeutic interventions.

The risk of valvular heart disease in the French Childhood Cancer Survivors' Study: Contribution of dose-volume histogram parameters

BACKGROUND AND PURPOSE

Valvular Heart Disease (VHD) is a known complication of childhood cancer after radiotherapy treatment. However, the dose-volume-effect relationships have not been fully explored.

MATERIALS AND METHODS

We obtained individual heart Dose Volume Histograms (DVH) for survivors of the French Childhood Cancer Survivors Study (FCCSS) who had received radiotherapy. We calculated the Mean Dose to the Heart (MHD) in Gy, as well as the heart DVH parameters (V_{d Gy}, which represents the percentage of heart volume receiving at least d Gy), fixing the thresholds to 0.1 Gy, 5 Gy, 20 Gy, and 40 Gy. We analyzed them furtherly in the subpopulation of the cohort that was treated with a dose lower than 5 Gy (V_0.1Gy|_V5Gy=0%), 20 Gy (V_5Gy|_V20Gy=0%), and 40 Gy (V_20Gy|_V40Gy=0%), respectively. We investigated their role in the occurrence of a VHD in this population-based observational cohort study using the Cox proportional hazard model, adjusting for age at cancer diagnosis and chemotherapy exposure.

RESULTS

Median follow-up was 30.6 years. Eighty-one patients out of the 7462 (1 %) with complete data experienced a severe VHD (grade ≥ 3). The risk of VHD increased along with the MHD, and it was associated with high doses to the heart (V_40Gy < 50 %, hazard ratio (HR) = 7.96, 95 % CI: 4.26-14.88 and V_20Gy|_V40Gy=0% >50 %, HR = 5.03, 95 % CI: [2.35-10.76]). Doses 5-20 Gy to more than 50 % (V_5Gy|_V20Gy=0% >50 %) of the heart induced a marginally non-significant estimated risk. We also observed a remarkable risk increase with attained age.

CONCLUSIONS

Our results provide new insight into the VHD risk that may impact current treatments and long-term follow-up of childhood cancer survivors.

New Insights into the Understanding of Mechanisms of Radiation-Induced Heart Disease

OPINION STATEMENT

Cancer patients who receive high-dose thoracic radiotherapy may develop radiation-induced heart disease (RIHD). The clinical presentation of RIHD comprises coronary artery atherosclerosis, valvular disease, pericarditis, cardiomyopathy, and conduction defects. These complications have significantly reduced due to the improved radiotherapy techniques. However, such methods still could not avoid heart radiation exposure. Furthermore, people who received relatively low-dose radiation exposures have exhibited significantly elevated RIHD risks in cohort studies of atomic bomb survivors and occupational exposures. The increased potential in exposure to natural and artificial ionizing radiation sources has emphasized the necessity to understand the development of RIHD. The pathological processes of RIHD include endothelial dysfunction, inflammation, fibrosis, and hypertrophy. The underlying mechanisms may involve the changes in oxidative stress, DNA damage response, telomere erosion, mitochondrial dysfunction, epigenetic regulation, circulation factors, protein post-translational modification, and metabolites. This review will discuss the recent advances in the mechanisms of RIHD at cellular and molecular levels.

Mediastinal irradiation and valvular heart disease

Anticancer therapy has the potential to cause unwanted cardiovascular side effects. Utilization of radiation therapy to treat tumors near the heart can result in radiation-induced valvular heart disease among other cardiovascular pathologies. The aim of this review is to describe the epidemiology, pathophysiology, risk prediction, non-invasive imaging modalities and management of radiation-induced valvular heart disease with a focus on pre-operative risk assessment and contemporary treatment options.

TRPM4 Participates in Irradiation-Induced Aortic Valve Remodeling in Mice

Simple Summary

Despite its benefit in cancer treatment, thoracic irradiation can induce aortic valve stenosis with fibrosis and calcification. The TRPM4 cation channel is known to participate in cellular remodeling including the transition of cardiac fibroblasts to myofibroblasts, similar to that observed during aortic valve stenosis. This study evaluates if TRPM4 is involved in irradiation-induced aortic valve damage. The aortic valve of mice was targeted by irradiation. Cardiac echography 5 months after treatment revealed an increase in aortic jet velocity, indicating stenosis. This was not observed in non-treated animals. Histological analysis revealed an increase in valvular cusp surface associated with fibrosis which was not observed in non-treated animals. The experiments were reproduced on mice after Trpm4 gene disruption. In these animals, irradiation did not induce valvular remodeling. It indicates that TRPM4 influences irradiation-induced aortic valve damage and thus could be a target to prevent such side effects of irradiation.

Abstract

Thoracic radiotherapy can lead to cardiac remodeling including valvular stenosis due to fibrosis and calcification. The monovalent non-selective cation channel TRPM4 is known to be involved in calcium handling and to participate in fibroblast transition to myofibroblasts, a phenomenon observed during aortic valve stenosis. The goal of this study was to evaluate if TRPM4 is involved in irradiation-induced aortic valve damage. Four-month-old Trpm4^+/+ and Trpm4^−/− mice received 10 Gy irradiation at the aortic valve. Cardiac parameters were evaluated by echography until 5 months post-irradiation, then hearts were collected for morphological and histological assessments. At the onset of the protocol, Trpm4^+/+ and Trpm4^−/− mice exhibited similar maximal aortic valve jet velocity and mean pressure gradient. Five months after irradiation, Trpm4^+/+ mice exhibited a significant increase in those parameters, compared to the untreated animals while no variation was detected in Trpm4^−/− mice. Morphological analysis revealed that irradiated Trpm4^+/+ mice exhibited a 53% significant increase in the aortic valve cusp surface while no significant variation was observed in Trpm4^−/− animals. Collagen staining revealed aortic valve fibrosis in irradiated Trpm4^+/+ mice but not in irradiated Trpm4^−/− animals. It indicates that TRPM4 influences irradiation-induced valvular remodeling.

Cardiac Remodelling Following Cancer Therapy: A Review

Cardiac remodelling is characterized by abnormal changes in the function and morphological properties such as diameter, mass, normal diameter of cavities, heart shape, fibrosis, thickening of vessels and heart layers, cardiomyopathy, infiltration of inflammatory cells, and some others. These damages are associated with damage to systolic and diastolic abnormalities, damage to ventricular function, and vascular remodelling, which may lead to heart failure and death. Exposure of the heart to radiation or anti-cancer drugs including chemotherapy drugs such as doxorubicin, receptor tyrosine kinase inhibitors (RTKIs) such as imatinib, and immune checkpoint inhibitors (ICIs) can induce several abnormal changes in the heart structure and function through the induction of inflammation and fibrosis, vascular remodelling, hypertrophy, and some others. This review aims to explain the basic mechanisms behind cardiac remodelling following cancer therapy by different anti-cancer modalities.

Uncoupling the Vicious Cycle of Mechanical Stress and Inflammation in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is a common acquired valvulopathy, which carries a high burden of mortality. Chronic inflammation has been postulated as the predominant pathophysiological process underlying CAVD. So far, no effective medical therapies exist to halt the progression of CAVD. This review aims to outline the known pathways of inflammation and calcification in CAVD, focussing on the critical roles of mechanical stress and mechanosensing in the perpetuation of valvular inflammation. Following initiation of valvular inflammation, dysregulation of proinflammatory and osteoregulatory signalling pathways stimulates endothelial-mesenchymal transition of valvular endothelial cells (VECs) and differentiation of valvular interstitial cells (VICs) into active myofibroblastic and osteoblastic phenotypes, which in turn mediate valvular extracellular matrix remodelling and calcification. Mechanosensitive signalling pathways convert mechanical forces experienced by valve leaflets and circulating cells into biochemical signals and may provide the positive feedback loop that promotes acceleration of disease progression in the advanced stages of CAVD. Mechanosensing is implicated in multiple aspects of CAVD pathophysiology. The mechanosensitive RhoA/ROCK and YAP/TAZ systems are implicated in aortic valve leaflet mineralisation in response to increased substrate stiffness. Exposure of aortic valve leaflets, endothelial cells and platelets to high shear stress results in increased expression of mediators of VIC differentiation. Upregulation of the Piezo1 mechanoreceptor has been demonstrated to promote inflammation in CAVD, which normalises following transcatheter valve replacement. Genetic variants and inhibition of Notch signalling accentuate VIC responses to altered mechanical stresses. The study of mechanosensing pathways has revealed promising insights into the mechanisms that perpetuate inflammation and calcification in CAVD. Mechanotransduction of altered mechanical stresses may provide the sought-after coupling link that drives a vicious cycle of chronic inflammation in CAVD. Mechanosensing pathways may yield promising targets for therapeutic interventions and prognostic biomarkers with the potential to improve the management of CAVD.

Radiation Induces Valvular Interstitial Cell Calcific Response in an in vitro Model of Calcific Aortic Valve Disease

Background: Mediastinal ionizing radiotherapy is associated with an increased risk of valvular disease, which demonstrates pathological hallmarks similar to calcific aortic valve disease (CAVD). Despite advances in radiotherapy techniques, the prevalence of comorbidities such as radiation-associated valvular disease is still increasing due to improved survival of patients receiving radiotherapy. However, the mechanisms of radiation-associated valvular disease are largely unknown. CAVD is considered to be an actively regulated disease process, mainly controlled by valvular interstitial cells (VICs). We hypothesize that radiation exposure catalyzes the calcific response of VICs and, therefore, contributes to the development of radiation-associated valvular disease.

Methods and Results: To delineate the relationship between radiation and VIC behavior (morphology, calcification, and matrix turnover), two different in vitro models were established: (1) VICs were cultured two-dimensional (2D) on coverslips in control medium (CM) or osteogenic medium (OM) and irradiated with 0, 2, 4, 8, or 16 Gray (Gy); and (2) three-dimensional (3D) hydrogel system was designed, loaded with VICs and exposed to 0, 4, or 16 Gy of radiation. In both models, a dose-dependent decrease in cell viability and proliferation was observed in CM and OM. Radiation exposure caused myofibroblast-like morphological changes and differentiation of VICs, as characterized by decreased αSMA expression. Calcification, as defined by increased alkaline phosphatase activity, was mostly present in the 2D irradiated VICs exposed to 4 Gy, while after exposure to higher doses VICs acquired a unique giant fibroblast-like cell morphology. Finally, matrix turnover was significantly affected by radiation exposure in the 3D irradiated VICs, as shown by decreased collagen staining and increased MMP-2 and MMP-9 activity.

Conclusions: The presented work demonstrates that radiation exposure enhances the calcific response in VICs, a hallmark of CAVD. In addition, high radiation exposure induces differentiation of VICs into a terminally differentiated giant-cell fibroblast. Further studies are essential to elucidate the underlying mechanisms of these radiation-induced valvular changes.

Runx2 (Runt-Related Transcription Factor 2) Links the DNA Damage Response to Osteogenic Reprogramming and Apoptosis of Vascular Smooth Muscle Cells

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Aortic valve stenosis and cancer: a common and complex association

Introduction. The prevalence of aortic valve stenosis (AS) and malignancy are both high, especially in elderly people and in developed countries. These two conditions frequently coexist and share the same risk factors as atherosclerotic disease.Area covered. The progression of calcified AS may be accelerated by both cardiovascular risk factors and cancer treatments, such as radiotherapy. The standard treatment for symptomatic severe AS is surgical aortic valve replacement; however, in cancer patients, transcatheter implantation may be preferred as they are often at high-risk for cardiac surgery. In patients with AS and cancer, physicians may face difficult treatment decisions.To date, there is limited information on the impact of malignancy on outcomes in patients with severe AS; hence, there is no established treatment policy.Expert Opinion. Treating clinicians must integrate complex information about the severity of valve disease and expected cardiac outcomes with information regarding the cancer prognosis and the need for specific treatment, including surgery. Other comorbidities, age and frailty also contribute to decision-making about whether, when, and how to perform aortic valve replacement.

Radiation-Associated Valvular Disease

PURPOSE OF REVIEW

Radiation-associated valvular disease (RAVD) is characterized by late valvular manifestations following radiation exposure to the mediastinum. Review of current guidelines was performed to examine best practices to reduce risk and optimize outcomes in this patient population.

RECENT FINDINGS

Early and consistent screening and comprehensive and careful planning are critical in managing RAVD. Due to long latency periods, serial screening and targeted evaluation of risk factors are essential to early detection. Varying and complex presentations of RAVD require an integrated team of experienced specialists equipped with multimodality imaging-based screening protocols to stratify risk, plan intervention, and evaluate treatment response. Patients with valvular manifestations associated with radiation therapy call for an individualized plan of care involving longitudinal multimodality imaging-based screening and experienced decision-making regarding timing and strategy of intervention to improve patient outcomes.

The Role of Echocardiography in the Cancer Patient

PURPOSE OF REVIEW

To review the uses of echocardiography in patients with cancer and how it has expanded beyond the typical monitoring of systolic function during potentially cardiotoxic cancer therapeutics.

RECENT FINDINGS

In addition to myocardial strain imaging being a predictor of subsequent left ventricular dysfunction, it can be used for pattern recognition to help identify patients with cardiac amyloidosis or Takotsubo cardiomyopathy. Echocardiography is essential for diagnosis and planning of intervention for aortic stenosis in radiation-induced valvular disease, for which transcutaneous aortic valve replacement that gives many cancer patients that are not surgical candidates an option for treatment. The safety of transesophageal echocardiography has recently been demonstrated in patients with cancer with thrombocytopenia and depleted white blood cell counts who are at increased risk of endocarditis. Echocardiography is an essential tool for evaluating common conditions in cancer patients such as pericardial disease, radiation-induced heart disease, and intracardiac tumors-with specific uses of specialized echocardiography techniques such as deformation imaging, transesophageal echocardiography, and point-of-care ultrasound.

Childhood cancer survivors: The integral role of the cardiologist and cardiovascular imaging

IMPORTANCE

With 80% of childhood cancer survivors (CCS) alive 30 years after diagnosis, preventable causes of death, such as cardiovascular disease resulting from initial cancer therapy, becomes an important metric. This leads to a more pronounced role for cardiologists in the care of CCS.

OBSERVATIONS

While routine cardiovascular screening has been traditionally performed by the hematologist/oncologist or primary care provider, our understanding of cardiovascular disease in CCS has advanced. The measurement of left ventricular ejection fraction (LVEF) can now be complemented with additional assessments of strain, LV mass, right ventricular function, diastolic function, valve function, the pericardium, coronary perfusion, and biomarkers. Risk factor modification, prophylaxis, and timing of treatment are also critical.

CONCLUSIONS AND RELEVANCE

Early cardiovascular screening and treatment in asymptomatic CCS can be nuanced and complex. As a result, there is a renewed opportunity for the cardiologist to play an integral role in the care of CCS.

KEY POINTS

Question/Purpose: Review cardiovascular disease and the role of the cardiologist in the care of asymptomatic childhood cancer survivors (CCS).

FINDINGS

Cardiovascular care in CCS benefits from a multi-faceted approach that does not overly rely on LVEF. Meaning: Adequate screening and treatment of cardiovascular disease in asymptomatic CCS may often be optimized by the involvement of a cardiologist.

Fibrotic aortic valve disease after radiotherapy: an immunohistochemical study in breast cancer and lymphoma patients

BACKGROUND

Radiation-associated aortic valve (AV) stenosis is frequently seen as a late sequela after thoracic radiotherapy (RT). Although the clinical relationship between thoracic radiotherapy and valvular dysfunction has been established, the process leading to accelerated aortic valve stenosis remains unclear. The aim of this study was to determine whether increased inflammatory cell infiltration, fibrosis, and calcification is present in aortic valves after radiotherapy at the time of aortic valve replacement.

METHODS

Stenotic aortic valve specimens from 43 patients were obtained after surgical aortic valve replacement. A total 28 patients had previously undergone radiotherapy for breast cancer or malignant lymphoma. A total 15 patients were included as control. The valve leaflets were assessed by (immuno)histochemistry for inflammatory cell composition (CD3, CD20, CD68, and CD163) and extracellular matrix changes (collagen and calcification).

RESULTS

Aortic valve cell density after radiotherapy for lymphoma was markedly decreased when compared with other groups. Irradiated aortic valve show similar (low) degrees of late T and B lymphocyte infiltration as control valves, whereas macrophage marker CD68 was decreased after radiotherapy for breast cancer. Collagen content was increased following radiotherapy. Aortic valves of patients with lymphoma contained significantly less calcified tissue when compared with the other groups.

CONCLUSION

High-dose radiation at a young age (patients with lymphoma) results in cell loss and premature fibrotic aortic valve stenosis as opposed to the degenerative calcific stenosis observed in patients with breast cancer. Our findings suggest a possible dose-dependent effect of radiotherapy on aortic valve fibrosis. The active presence of inflammatory cells may be limited to the acute phase after radiotherapy.

Radiation-Associated Cardiac Disease: From Molecular Mechanisms to Clinical Management

PURPOSE OF REVIEW

Radiation-associated cardiac disease (RACD) is an increasingly recognized latent manifestation of chest and mediastinal radiation therapy. The delayed presentation reflects increased survival rates from malignancies successfully treated decades previously. However, individuals are now presenting with multiple coexistent manifestations of RACD and pulmonary disease as a consequence of high-dose radiation administered prior to the routine institution of modern dose-modulating regimens. Increased awareness of RACD is critical for implementation of appropriate screening algorithms and for specific management strategies involving the timing and strategies of intervention in these patients.

RECENT FINDINGS

Recent advances in multimodality cardiac imaging have demonstrated pathognomonic findings of RACD, which can predict outcomes including mortality. Accurate diagnosis of these typically concurrent manifestations is critical and should prompt referral to a center experienced in managing RACD as surgical risk is significantly increased for this patient cohort, particularly for those undergoing redo operation. The latent effect of RACD and its unique combination of manifestations means that these patients will increasingly present with challenging management issues, resulting in increased rates of morbidity and mortality. Timing of treatment intervention must be carefully considered, although percutaneous options may provide alternative future strategies for this higher risk cohort.

Radiation induced valvular disease: the internist’s prospective

Radiation-induced cardiac injury entails a wide spectrum of cardiovascular complications such as cardiomyopathy and valvular diseases among others. We present the internist’s perspective and the challenges faced in managing these patients. There are guidelines addressing radiation-induced valvular disease (RIVD) including screening and treatment, but are often unrecognised by most internist’s practice. A thorough cardiovascular examination and screening echocardiography may detect RIVD at an earlier stage. Early screening with transthoracic echocardiogram should be considered in asymptomatic or low-risk patients and more frequently in symptomatic and high-risk patients. The internists should educate their patients with prior chest irradiation, regarding the possible radiation related adverse cardiovascular effects and recommended screening. Lifestyle changes and aggressive cardiovascular risk modification should be emphasised, as concomitant hypertension, coronary artery disease and cardiomyopathy can have unfavourable effects in these patients.

The shift of macrophages toward M1 phenotype promotes aortic valvular calcification

OBJECTIVE

The purpose of the present study was to comprehensively compare the phenotype profile of infiltrated macrophages in human noncalcified and calcific aortic valves, and to determine whether the shift of macrophage polarization modulates valvular calcification in vitro.

METHODS

Cell surface markers of macrophages and inflammatory cytokines expression in 90 cases of human noncalcified and calcific aortic valve leaflets were analyzed. The normal aortic valve interstitial cells were isolated and cultured in vitro. After incubation with nonconditioned medium and conditioned medium from unstimulated or lipopolysaccharide-stimulated U937 monocytes, valve interstitial cells were evaluated by osteogenic differentiation markers.

RESULTS

Infiltration of macrophages was enhanced in the calcific aortic valves, and M1 phenotype was the predominant macrophage subsets. In addition, both proinflammatory and anti-inflammatory cytokines were significantly upregulated in the calcific aortic valves. Furthermore, lipopolysaccharide-stimulated monocytes presented with increased expression of inducible nitric oxide synthase and high proportional CD11c-positive (M1) macrophages. Conditioned medium from unstimulated monocytes promoted the osteogenic differentiation of valve interstitial cells in vitro, as evidenced by increased markers such as bone morphogenetic protein 2, osteopontin, and alkaline phosphatase. Conditioned medium from M1 macrophages further enhanced valve interstitial cells calcification. Enzyme-linked immunosorbent assay showed that M1 phenotype macrophages secreted tumor necrosis factors α and interleukin 6, and neutralizing antibodies to these 2 proinflammatory cytokines attenuated induction of osteogenic differentiation and calcification by the conditioned media.

CONCLUSIONS

Both total numbers and polarization of macrophage influence the process of calcification in human aortic valve. The shift toward M1 phenotype might promote valve interstitial cell calcification.

Radiation Toxicity to the Cardiovascular System

Radiation therapy is an important component of cancer treatment, and today, it is applied to approximately 50% of malignancies, including valvular, myocardial, pericardial, coronary or peripheral vascular disease, and arrhythmias. An increased clinical suspicion and knowledge of those mechanisms is important to initiate appropriate screening for the optimal diagnosis and treatment. As the number of cancer survivors has been steadily increasing over the last decades, cardio-oncology, an evolving subspecialty of cardiology, will soon play a pivotal role in raising awareness of the increased cardiovascular risk and formulate strategies to optimally manage patients in this unique population.

Radiation-induced valvular heart disease

Radiation to the mediastinum is a key component of treatment with curative intent for a range of cancers including Hodgkin's lymphoma and breast cancer. Exposure to radiation is associated with a risk of radiation-induced heart valve damage characterised by valve fibrosis and calcification. There is a latent interval of 10-20 years between radiation exposure and development of clinically significant heart valve disease. Risk is related to radiation dose received, interval from exposure and use of concomitant chemotherapy. Long-term outlook and the risk of valve surgery are related to the effects of radiation on mediastinal structures including pulmonary fibrosis and pericardial constriction. Dose prediction models to predict the risk of heart valve disease in the future and newer radiation techniques to reduce the radiation dose to the heart are being developed. Surveillance strategies for this cohort of cancer survivors at risk of developing significant heart valve complications are required.

Transcatheter Aortic Valve Implantation in a Woman with Porcelain Aorta, Previous Sternotomy for Coronary Artery Bypass Grafting, and Critical Aortic Stenosis

A 74-year-old woman who was diagnosed with right breast cancer at age 39 had been treated with mastectomy, and repeated cycles of chemotherapy and radiotherapy. She also had a history of coronary artery disease, wherein two coronary artery bypass grafts were performed 3 years ago. At that time, porcelain aorta was detected during surgery. In the year prior to admission, the patient presented with severe symptomatic critical aortic stenosis. Due to the prohibitively high surgical risk and need for aortic valve replacement, she underwent successful transcatheter aortic valve implantation with transfemoral implantation of a 29 mm Medtronic CoreValve prosthesis. The patient experienced a good result with reduction of the transaortic gradient and mild residual aortic regurgitation.

KEY WORDS

Aortic stenosis; Coronary artery bypass grafting; Porcelain aorta; Radiation; Transcatheter aortic valve implantation.

Epigenetics in radiation-induced fibrosis

Radiotherapy is a major cancer treatment option but dose-limiting side effects such as late-onset fibrosis in the irradiated tissue severely impair quality of life in cancer survivors. Efforts to explain radiation-induced fibrosis, for example, by genetic variation remained largely inconclusive. Recently published molecular analyses on radiation response and fibrogenesis showed a prominent role of epigenetic gene regulation. This review summarizes the current knowledge on epigenetic modifications in fibrotic disease and radiation response, and it points out the important role for epigenetic mechanisms such as DNA methylation, microRNAs and histone modifications in the development of this disease. The synopsis illustrates the complexity of radiation-induced fibrosis and reveals the need for investigations to further unravel its molecular mechanisms. Importantly, epigenetic changes are long-term determinants of gene expression and can therefore support those mechanisms that induce and perpetuate fibrogenesis even in the absence of the initial damaging stimulus. Future work must comprise the interconnection of acute radiation response and long-lasting epigenetic effects in order to assess their role in late-onset radiation fibrosis. An improved understanding of the underlying biology is fundamental to better comprehend the origin of this disease and to improve both preventive and therapeutic strategies.

Cardiovascular complications of radiotherapy

Chest radiotherapy is routinely used to treat malignancies such as Hodgkin disease and breast cancer but is commonly associated with a variety of cardiovascular complications involving the pericardium, myocardium, valves, coronary arteries, and conduction system. Cardiovascular complications are related to the total dose of radiation and the fractionation of the dose. They are usually progressive, portend poor prognosis, and are often refractory to treatment after significant radiation exposure. The mechanism of injury is multifactorial and likely involves endothelial damage of the microvasculature and coronary arteries and liberation of multiple inflammatory and profibrotic cytokines. In conclusion, routine follow-up with a cardiologist, which might include screening for valvular disease with echocardiography and coronary artery disease with computed tomography angiography or coronary artery calcium scoring, should be considered in patients with a history of chest radiotherapy.

Understanding radiation-induced cardiovascular damage and strategies for intervention

There is a clear association between therapeutic doses of thoracic irradiation and an increased risk of cardiovascular disease (CVD) in cancer survivors, although these effects may take decades to become symptomatic. Long-term survivors of Hodgkin's lymphoma and childhood cancers have two-fold to more than seven-fold increased risks for late cardiac deaths after total tumour doses of 30-40 Gy, given in 2 Gy fractions, where large volumes of heart were included in the field. Increased cardiac mortality is also seen in women irradiated for breast cancer. Breast doses are generally 40-50 Gy in 2 Gy fractions, but only a small part of the heart is included in the treatment fields and mean heart doses rarely exceeded 10-15 Gy, even with older techniques. The relative risks of cardiac mortality (1.1-1.4) are consequently lower than for Hodgkin's lymphoma survivors. Some epidemiological studies show increased risks of cardiac death after accidental or environmental total body exposures to much lower radiation doses. The mechanisms whereby these cardiac effects occur are not fully understood and different mechanisms are probably involved after high therapeutic doses to the heart, or part of the heart, than after low total body exposures. These various mechanisms probably result in different cardiac pathologies, e.g. coronary artery atherosclerosis leading to myocardial infarct, versus microvascular damage and fibrosis leading to congestive heart failure. Experimental studies can help to unravel some of these mechanisms and may identify suitable strategies for managing or inhibiting CVD. In this overview, the main epidemiological and clinical evidence for radiation-induced CVD is summarised. Experimental data shedding light on some of the underlying pathologies and possible targets for intervention are also discussed.